1. Field of the Invention
This invention relates generally to photographic imaging and methods therefor and, more particularly, to a computerized multicolor electronic camera and method therefor comprising a computer-controlled electronic image sensor which requires less light to produce an analog image of an object than a conventional electronic camera, provides a digital signal representation of said analog image or a portion thereof that is stored in the camera, eliminates pixel jitter, and is capable of transfering said digital signal representation to a host computer using a Small Computer System Interface (SCSI). Said computerized camera furthermore provides digital correction of photometric nonlinearities in said digital representation of said analog image, provides exposure control at each of a multiplicity of colors in order to compensate for the non-uniform spectral response of said image sensor, and generates real-time monocolor video on command to assist the user in focusing.
2. Description of the Prior Art
Photographic images are an essential part of almost every aspect of diagnosis, teaching, and publication in medical fields, such as the field of pathology. When photographic images are included as reference material for teaching, for example, they are typically stored as a 35 millimeter transparencies. A pathologist in a teaching hospital, for example, may have on file as many as 100,000 transparencies. Since the transparencies themselves are not in electronic form, computerized storage and retrieval techniques are not applicable to such files.
To obtain an electronic representation of an image of a microscopic specimen, a pathologist may utilize a video camera connected to a microscope to display, on a cathode ray tube, an image of said specimen magnified through the microscope. Alternatively, to obtain an electronic representation of the image of a gross specimen, a pathologist may use a video camera mounted on a tripod with the image of said specimen produced using a standard video camera lens. It should be noted that in both cases the quality of the electronic representation of the image should be similar to that which is obtainable when a 35 millimeter camera is connected to record a photographic image of said specimen.
According to the prior art, the best electronic representation of an image of a specimen was previously generated by utilizing a studio quality video camera. As is well known to those skilled in the art, the studio camera has a notoriously low sensitivity to light. Therefore, in practice, a high illumination level is maintained. This high illumination level may bleach a microscopic specimen and thereby damage it. Further, a high illumination level can cause discomfort to the pathologist viewing the specimen.
To obtain a digital signal representation of an electronic representation of an image of a specimen the video output of a studio camera must be connected to what is known in the art as a "frame grabber" that digitizes a selected frame, thereby generating a digital signal representation of the video image. Most digital computers do not provide for the direct installation of a frame grabber but do frequently provide a SCSI (Small Computer Systems Interface) connection to external digital devices. Therefore, in practice, a frame graber-SCSI interface must be used to provide the digital signal representation of the image.
The studio camera usually operates at a 30 frame per second rate using analog voltages to generate analog horizontal and vertical timing signals that are required to scan the analog electronic image produced on the photosensitive surface within the camera and generate the analog electronic signal representation in a form suitable for display on a cathode ray tube. Analog horizontal and vertical timing signals are notoriously inaccurate so that the electronic signal representation of the image varies spatially from frame to frame. This is known in the art as "pixel jitter." If the studio camera were computerized so that the vertical and horizontal timing signals were digitally generated and therefore precise, then pixel jitter would be eliminated.
It is well known to those skilled in the art that the photosensitive surface within a studio camera exhibits photometric nonlinearities in that the analog value of the electronic signal representation of an image is not linearly proportional to the intensity of the incident light. If the studio camera were computerized, its photometric nonlinearities could be compensated by digital means.
Further, a studio camera is notoriously inaccurate in its spectral response in that the analog value of the electronic signal representation of an image varies nonlinearly as a function of the wavelength of the incident light energy. If the studio camera were computerized, its nonlinear spectral responsivity could be compensated by supplying a digitally controlled exposure for each wavelength.
As is well known to those skilled in the art, current implementations of the SCSI standard do not accomodate data transfer at a rate suitable for the transmission of real-time video data from a studio camera. Therefore, computerization of a studio camera and use of a SCSI interface would significantly slow the generation of the electronic signal representation of an image. This would make it difficult for a pathologist to focus the image. However, by providing an asynchronous operating mode for the computerized studio camera for the purpose of generating an electronic signal representation of the image on a cathode ray tube in real-time, the image could easily be focused prior to digitization. Furthermore, by permitting the pathologist to focus images corresponding to each spectral color of a full-color image separately, it would be possible to correct for the chromatic aberration of a microscope lens or video camera lens.
A studio camera is usually inconveniently large. Both the studio camera and the associated frame grabber are expensive. Computerized studio cameras not requiring frame grabbers are unavailable. Accordingly, a need exists for a small, relatively inexpensive, computerized multicolor camera that operates at any light level both to minimize damage to a specimen, the image of which is being recorded, and to reduce discomfort to the observer. Further, a need exists for such a computerized multicolor camera to be of a type that produces digital horizontal and vertical timing signals so that pixel jitter is eliminated. Also, a need exists for such a computerized multicolor camera to be of a type that provides an exposure control at each of several selected wavelengths combined in a manner to compensate for nonuniformities in the spectral response of the camera. Additionally, a need exists for such a computerized camera to be of a type that provides a digital signal representation of an image of an object via a SCSI interface to a host computer. Finally, there is a need for such a camera to produce real-time monocolor video at one or more of the selected wavelengths for focusing.